1. Field of the Invention
Aspects of the invention generally relate to the fabrication of semiconductor devices and to chemical mechanical polishing and planarization of semiconductor devices.
2. Description of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large-scale integration (VLSI) and ultra large-scale integration (ULSI) of semiconductor devices. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias, contacts, lines, and other interconnects. Reliable formation of these interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
In order to further improve the current density of semiconductor devices on integrated circuits, it has become necessary to use conductive materials having low resistivity for conductors and materials having low dielectric constant (low k, defined herein as having dielectric constants, k, less than about 4.0) as insulating layers to reduce the capacitive coupling between adjacent interconnects. Increased capacitative coupling between layers can detrimentally affect the functioning of semiconductor devices.
One conductive material gaining acceptance is copper and its alloys, which have become the materials of choice for sub-quarter-micron interconnect technology because copper has a lower resistivity than aluminum, (1.7 xcexcxcexa9-cm compared to 3.1 xcexcxcexa9-cm for aluminum), a higher current and higher carrying capacity. These characteristics are important for supporting the higher current densities experienced at high levels of integration and increased device speed. Further, copper has a good thermal conductivity and is available in a highly pure state.
One difficulty in using copper in semiconductor devices is that copper is difficult to etch and achieve a precise pattern. Etching with copper using traditional deposition/etch processes for forming interconnects has been less than satisfactory. Therefore, new methods of manufacturing interconnects having copper-containing materials and low k dielectric materials are being developed.
One method for forming vertical and horizontal interconnects is by a damascene or dual damascene method. In the damascene method, one or more dielectric materials, such as the low k dielectric materials, are deposited and pattern etched to form the vertical interconnects, i.e., vias, and horizontal interconnects, i.e., lines. Conductive materials, such as copper-containing materials, and other materials, such as barrier layer materials used to prevent diffusion of copper-containing materials into the surrounding low k dielectric, are then inlaid into the etched pattern. Any excess copper-containing materials and excess barrier layer material external to the etched pattern, such as on the field of the substrate, is then removed.
As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or xe2x80x9cpolishingxe2x80x9d a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in dual damascene processes to remove excess deposited material and to provide an even surface for subsequent levels of metallization and processing. Planarization may also be used in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing article in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the substrate against the polishing media. The article is moved relative to the substrate by an external driving force. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of the substrate and the polishing article while dispersing a polishing composition to effect both chemical activity and mechanical activity.
Conventionally, in polishing copper features, such as dual damascene features, the copper-containing material, and a portion of the barrier layer, is polished to the level of the barrier layer, and then the barrier layer is polished, with a portion of the dielectric layer and copper features, to a level of the underlying dielectric layer using abrasive polishing solutions. However, such a polishing process often results in uneven removal of copper in features and the dielectric layer resulting is the formation of topographical defects, such as concavities or depressions in the features, referred to as dishing, and removal of dielectric material surrounding features, referred to as erosion.
FIG. 1 is a schematic view of a substrate illustrating the phenomenon of dishing. Conductive lines 11 and 12 are formed by depositing conductive materials, such as copper or copper alloy, in a feature definition formed in the dielectric layer 10, typically comprised of silicon oxides or other dielectric materials. After planarization, a portion of the conductive material is depressed by an amount D, referred to as the amount of dishing, forming a concave copper surface. Dishing results in a non-planar surface that impairs the ability to print high-resolution lines during subsequent photolithographic steps and detrimentally affects subsequent surface topography of the substrate and device formation. Dishing also detrimentally affects the performance of devices by lowering the conductance and increasing the resistance of the devices, contrary to the benefit of using higher conductive materials, such as copper.
One solution is to polish copper material by using abrasive-free polishing compositions. However, abrasive-free polishing compositions may be unable to sufficiently remove all of the desired copper materials from a substrate surface, such as at the interface between copper and the barrier layer, which is generally non-planar. Such copper materials retained on the substrate surface, or residues, can detrimentally affect device formation, such as creating short-circuits within or between devices, and thereby reduce device yields and reduce substrate throughput, as well as detrimentally affect the polish quality of the substrate surface.
One solution to ensure removal of all the copper material including copper residues before removing the barrier material is to overpolish the copper and the interface. However, overpolishing of the interface with abrasive-free polishing compositions have not been successful in removing copper residues, and removal of those residues often require extensive polishing times, which have resulted in increased operating costs and decreased substrate throughput.
Therefore, there exists a need for an apparatus, and method that facilitates the removal of copper-containing material from the surface of a substrate with minimal or reduced dishing and with essentially no residues remaining after polishing.
Aspects of the invention relate generally to methods and apparatus for polishing conductive materials with low dishing of features and essentially no residual conductive material between features. In one aspect, a method is provided for processing a substrate including providing a substrate having a conductive material disposed thereon to a polishing apparatus, polishing the substrate at a first relative linear velocity between about 600 mm/second and about 1900 mm/second at the center of the substrate, and polishing the substrate at a second relative linear velocity between about 100 mm/second and about 550 mm/second at the center of the substrate.
In another aspect, a method is provided for processing a substrate including providing a substrate to a polishing apparatus having one or more rotational carrier heads and one or more rotatable platens, polishing the substrate to remove bulk conductive material, and polishing the substrate by a ratio of carrier head rotational speed to platen rotational speed of between about 2:1 and about 3:1 to remove residual conductive material.
In another aspect, a method is provided for processing a substrate including providing a substrate comprising feature definitions formed in a dielectric layer, a tantalum containing material deposited on the dielectric layer and in the feature definitions, and copper material deposited on the tantalum containing material and filling the feature definitions, to a polishing apparatus having one or more rotational carrier heads and one or more rotatable platens, supplying a first polishing composition to the polishing apparatus at a flow rate of about 200 ml/min or greater, polishing the substrate at a first relative linear velocity between about 600 mm/second and about 1900 mm/second at the center of the substrate to remove bulk copper material, supplying a second polishing composition to the second polishing platen at a flow rate between about 10 ml/min and less than about 110 ml/min, polishing the substrate at a platen rotational speed between about 10 rpms and about 40 rpms and a carrier head rotational speed between about 20 rpms and about 120 rpms to provide a second relative linear velocity between about 100 mm/second and about 550 mm/second at the center of the substrate, wherein the carrier head rotational speed is greater than the platen rotational speed by a ratio of carrier head rotational speed to platen rotational speed of between about 2:1 and about 3:1 to remove residual copper material, and then polishing the substrate to remove the barrier layer.